1. Field of the Invention
The present invention relates to an aqueous cleaning solution for removing contaminants from the surface of an integrated circuit substrate and a cleaning method using the same.
2. Background of the Related Art
Patterns of various interconnections comprising aluminum, titanium or titanium nitride, and contact holes or via holes exposing the interconnection patterns, must be formed on a substrate to complete an integrated circuit. The interconnection patterns, the contact holes and the via holes are formed through successive photo lithography, etching, ashing, cleaning, rinsing and drying processes.
The ashing process is a dry strip process for removing a resist pattern used as a mask during etching. The cleaning process is for removing contaminants, such as etching residues generated during the etching or the ashing process, for forming the interconnection pattern or the contact hole (via hole) from a surface of the integrated circuit substrate. The residues to be removed are organic polymers formed by reacting carbon C, hydrogen H or oxygen O which form a resist pattern, with an interconnection material and plasma during reactive ion etching (RIE), organic metallic polymers formed by back-sputtering the interconnection material to the sidewalls of the resist pattern and to the contact hole or to the via hole during the etching or ashing, resist residues remaining on the surface of the substrate after ashing, and an insulating material or a metallic insulating material formed by back-sputtering the insulating layer under the interconnection pattern which is exposed by over-etching.
An organic cleaning solution including a polar solvent such as alcohol, a basic amine reducing agent such as hydroxylamine, an organic acid such as catechol and a corrosion inhibitor are widely used for the cleaning solution.
However, the conventional organic cleaning solution is generally used at a high temperature of 60xc2x0 C. or more to have the desired cleaning effects, so that the organic cleaning solution is vaporized which thus shortens its useable life span. Meanwhile, the cleaning solution includes a reducing agent such as a basic amine having a relatively low reducing ability, so that the etching residues such as the organic metallic polymer of a tungsten oxide or a copper oxide, which are generated during the etching of a new interconnection such as a tungsten interconnection or a copper interconnection, cannot be completely removed. Thus, the step of processing a cleaning reinforcing agent, e.g., a nitric acid may be required as a pre-ashing step to completely remove the etching residues.
Also, the conventional organic cleaning solution includes an organic component, so that when rinse is performed with only deionized water, the organic components cannot be completely removed and thus remain on the substrate. Thus, the interconnection film can be easily corroded thereby changing the profile of the interconnection pattern. Thus, a rinse process using a rinse containing alcohol such as isopropyl alcohol (IPA) is additionally required before the rinse process using deionized water. Thus, the conventional environments for the manufacturing equipment and cleaning processes are complicated. Also, the organic cleaning solution easily corrodes metals, thereby damaging the pipes carrying the cleaning solution and the cleaning equipment.
Moreover, as described above, in order to strengthen the ability to remove impurities and suppress the corrosion of the interconnection layer, the nitric acid treatment step is performed before the ashing process, or the IPA rinser treatment step must be performed before the rinse process using deionized water. This complicates the process and increases the process time, thereby reducing productivity. Also, the cleaning reinforcing agent (nitric acid) and rinser (IPA) as well as an organic cleaning solution are further required, so that the total production cost is increased. In addition, respective steps require respective baths, so that the manufacturing equipment becomes unnecessarily bulky. Also, organic cleaning solutions must be disposed of after several uses, and the disposal cost is added to the total process cost.
Also, the conventional organic cleaning solution has a low removing ability with respect to an oxide layer. As shown in FIGS. 1A and 1B, an oxide layer 20 under an interconnection pattern 30 is overetched and re-sputtered during an etching process for forming the interconnection pattern 30 on a substrate 10, and thus the re-sputtered oxide layer 50 is attached to a surface of an organic polymer 40 which has been attached to a sidewall of the interconnection pattern 30. When a conventional organic cleaning solution is used, the polymer 40 is removed while the oxide layer 50 is not completely removed. Thus, as shown in FIG. 2, the re-sputtered oxide layer 50 may lay across the adjacent interconnection patterns 30. Here, the re-sputtered oxide layer 50 is mostly a metallic oxide layer contaminated by a conductive material generated by etching, to thereby generate a bridge phenomenon between interconnections.
It is an objective of the present invention to provide a cleaning solution having an excellent ability for removing contaminants from the surface of an integrated circuit substrate, without damaging a conductive layer.
It is another objective of the present invention to provide a method for removing contaminants from the surface of the integrated circuit substrate using the cleaning solution.
Accordingly, to achieve the first objective, the cleaning solution according to the present invention includes a fluoride reducing agent, an organic acid containing a carboxyl group, an alkaline pH controller and water. The range of the pH of the cleaning solution is 3.5-8.8.
The fluoride reducing agent may be a hydrofluoride (HF), a hydroboron tetrafluoride (HBF4) or ammonium fluoride (NH4F), the organic acid may be acetic acid (CH3COOH) or citric acid (C3H4(OH)(COOH)3), and the alkaline pH controller may be ammonium hydroxide (NH4OH), potassium hydroxide (KOH), tetramethylammonium hydroxide ((CH3)4NH4OH) or tetraethylammonium hydroxide ((CH3CH2)4NH4OH).
The content of the fluoride reducing agent is 0.01-1 weight % of the total weight of the cleaning solution, the content of the organic acid containing a carboxyl group is 1-50 weight % of the total weight of the cleaning solution and the content of the alkaline pH controller is 0.25-15 weight % of the total weight of the cleaning solution.
To achieve the second objective, the method for removing impurities from an integrated circuit substrate includes the step of applying a cleaning solution to the surface of the integrated circuit substrate wherein the cleaning solution contains a fluoride reducing agent, an organic acid containing a carboxyl group, an alkaline pH controller and water.
The contaminants are at least of one an etching residue, polymer, an organic metallic polymer, a silicon oxide layer or a contaminated silicon oxide layer, and the surface of the integrated circuit substrate is partially metallic.
According to the cleaning solution of the present invention, the organic polymer, the organic metallic polymer and the oxide layer can be effectively removed and the conductive layer is not damaged.